Page 221 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Reciprocating Gas Engines and Compressors 203

engine and/or compressor outage. The reader may refer to Volume 2 of
this series for details on instrumentation and analysis.
Ignition has for years been the critical part of an engine, but with the
pulse generator and transistorized equipment, problems will be fewer in
the future. As a matter of fact, if progress could be made on the life and
reliability of spark plugs, the trouble-free day for ignition systems would
not be too far off.
Turbochargers and Blowers-Any part of the engine involved in fur-
nishing air for combustion is very important. Most modern engines have
rotating equipment for that purpose and, although they operate at high
speeds, their life and service are very acceptable if they are properly
maintained. When trouble does occur with turbochargers or blowers, vi-
bration is one of the first signs. However, this can be detected long before
damage sets in by checking each month with any one of the many instru-
ments available today. If an instrument is not allocated to the installation,
the ends of the fingernails are sensitive- enough to feel vibration before
damage is done. This check does not require any time; therefore, it can
be done every day.
A common problem with turbochargers is carbon formation on the tur-
bine end that finally takes up end-thrust clearance, resulting in complete
damage to the very expensive rotor. To guard against this, the rotor end
play should be checked at least every three months. If an inspection win-
dow is provided, the check can be made without any disassembly. Oil
leaks at the front end and air-impeller fouling sometimes cause problems ,
but this can be determined through the inspection window. The limiting
factor for any turbocharger is exhaust inlet temperature. Therefore, the
engine builder’s maximum should not be exceeded. The turbocharger
output remains fairly constant (depending on atmospheric conditions)
with engine load and speed. Any decrease or increase in turbocharger
speed is reason for concern. The instrument used for checking vibration
should be one that records speed as well as amplitude of vibration,
The spin-down test requires very little time and is so convenient and
informative that it is a “must” for maintaining this type of equipment.
This test amounts to recording the time it takes the rotor to come to rest
after the engine throttle is shut off. This reading can be taken any time
during a scheduled shutdown. It is better to do it at no load and rated
engine speed. As the throttle is moved, the stop watch can be started. The
operator will have plenty of time to get around to the inspection window
of the turbocharger because it generally takes four to five minutes for the
rotor to stop.
Engine Balance-The term “engine balance” means that each power
cylinder should produce its equal share of power. Everyone in the trade is